A High Power Set-up to Test Optical Coatings

To detect gravitational waves, the LIGO detectors need to limit the noise from multiple sources. Noise related to the quality and characteristics of the coating that is used on the test masses is one of the most important and most difficult to mitigate. Significant effort is invested in finding new types of coatings that satisfy the many stringent requirements of LIGO, which include low thermal noise, low scattering and low absorption. In addition, these coatings need to withstand high CW power without exhibiting any significant deterioration. It is therefore crucial to develop optical set-ups that will measure all the relevant coating properties, and under conditions similar to LIGO. Here we describe one such set-up at Bard College. The main characteristics of our set-up include a high finesse cavity inside an ultra-high vacuum chamber, in which mirror samples will be tested for scattering and aging over long periods of time.